Textile



Nov.- 12, 1963 v scd 3,110,617

TEXTILE Filed May 20, 1960 IG. I

NVENTO PAUL SCOTT v Y W617 A ORNEY United States Patent 3,110,617 TEXTHLE Paul T. Scott, Kinston, N.., assignor to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Deiaware Filed May 26, 1960, Ser. No. 30,623 9 Claims. (Cl. 117138.8)

This invention is concerned with a method of processing synthetic thermosplastic fibers. More particularly it is concerned with the prevention of coalescing of filaments during high temperature processing of synthetic linear polyester textile yarns.

In the manufacture and processing of textile filaments from synthetic linear polyesters, it is frequently desirable to subject the filaments to high temperature conditions. For example, Leben and Little in British Patent 603,840 suggested that polyester filaments of the type disclosed by Whinfield and Dickson in US. 2,465,319 may be oriented by drawing at temperatures up to 30 below their melting point. Again, Pace in U.S. 2,578,- 899 taught that synthetic linear polyester filaments may be super-stretched from ten to seventy-five times their original length if heated to a temperature between 20 and 60 C. above the apparent minimum crystallization temperature of the amorphous polyester.

In attempting to derive a commercially feasible superstret'ching process from the invention of Pace by preheating undrawn amorphous polyethylene terephthalate yarn on a hot roller, rather than in the oil bath exemplified by Pace, it has been discovered that the individual filaments in a multi filament yarn bundle become fused together and remain fused throughout subsequent yarn processing steps. This fusing or coalescing of filaments results in a stiff yarn similar to a monofil and produces boardy, stiff, and unattractive fabrics. Precoating the filaments with oil or other spin finishes known to the art or with high melting inert solids such as talc does not prevent the coalescing of the filaments in such high temperature treatments.

Therefore, it is an object of this invention to provide a method of preventing the coalescing of filaments during the high temperature treatment of undrawn amorphous linear polyester yarns.

Another object is the prevention of fusing of filaments when synthetic linear polyester yarns are stretched from a heated roller.

Other objects will be apparent from the detailed discussion of the invention which follows.

It has now been found that the fusion of filaments which normally occurs upon contacting synthetic linear polyester multi-filament yarn with a hot surface, maintained at a temperature above the softening point of amorphous polymer, can be effectively prevented there is applied to the surface of the filaments a minor amount of an alkaline compound capable of reacting with the polyester.

Accordingly, the objects of this invention are obtained by a process which comprises depositing upon the surfaces of solid undrawn filaments of a synthetic linear polyester multifilament yarn, prior to a heating step, a salt including hydroxides and hydrated oxides in which the cation is a metal from the group consisting of the alkali and alkaline-earth metals and the anion is hydroxyl or an anion derived from a week acid capable of being vaporized, sublimed, or decomposed at a temperature below the melting point of the polyester.

FIGURE 1 illustrates a magnified view of the cross section of a polyester yarn drawn at a high temperature with a high degree of filament fusing.

FIGURE 2 illustrates a magnified view of the cross section of a polyester yarn drawn at a high temperature 3,11%,61? Patented N ov. 12, l 963 ice while protected by the present invention. In both figures each circle represents a filament end.

The minimum temperature at which the process of this invention becomes useful is the softening temperature of the undrawn filaments, or, more specifically, the minimum temperature at which two undrawn filaments can be made to stick together. Generally, the softening temperature of polyesters is substantially equal to T +10 C. where T is the minimum temperature of crystallization defined by Pace in US. 2,578,899. For polyethylene terephthalate filaments, the softening temperature is about C. It is to be understood that temperature of importance here is the actual temperature of the polyester filament, which may or may not be the same as the temperature of the heating element being contacted by the filament.

In the process of this invention the salt may be applied to the filament bundle at any time or in any stage of processing prior to the time the yarn encounters the heated surface which normally would cause the coalescing of filaments. Preferably the salt is applied to the yarn in the form of a dilute solution in a solvent which is subsequently vaporized, leaving the salt deposited uniformly on the surfaces of the filaments. Advantageously the salt is dissolved in spin finish and applied to the yarn bundle during the spinning operation. Alternatively the salt may be applied to the yarn after the spinning opera-tion by contacting the yarn with a liquid solution of the salt.

The salt solution may be applied to the yarn in any of the ways known to the art: The salt solution may be sprayed on the yarn; the yarn may be immersed momentarily in the salt solution; or the yarn may be passed over a rotating roller which is partially immersed in the salt solution. Other procedures for applying the salt to the yarn will come readily to mind.

Salts which are operable in the process of this invention are particularly those of the alkali and alkaline-earth metals of groups I and II including magnesium but not beryllium in the periodic table. The most important and preferred metals of these groups because of availability and price, are sodium, potassium, magnesium and calcium. Other metals which may be used include lithium, rubidium and cesium as well as strontium, barium, and radium. Salts having volatile cations such as NH, salts, amines, etc., do not produce comparable results.

The anions of salts operable in this invention are par ticularly characterized in that they are derived from weak acids. The term weak acid is intended to include all those acids having an ionization constant K less than about 0.25, measured in water at 18 C. Ionization constant is defined by the equation for the reaction HASH++A where [HA] is the concentration of the unionized acid, [I-I+] is the concentration of hydrogen ions, and [A] is the concentration of acid anions. The term acid is used in its broader sense, i.e., a compound containing hydrogen in which the hydrogen can be replaced by a metal or a basic radical. Thus, the term acid includes Water and the alcohols, as well as the more familiar acids such as acetic, oxalic and propionic acids.

Salts operable in the process of this invention are further characterized in that their anions may be removed in part from the sphere of reaction, particularly those anions from acids which vaporize, sublime, or decompose below the melting temperature of the polyester. Specifically, the salts should have an anion derived from a weak acid which has a boiling point, sublimation point, or decomposition point less than about 250 C. with 3 most polyesters. A salt with an anion derived from other acids which do not have a boiling point, a sublimation point, or a decomposition point below the melting point of the polyester filaments is not operable in the process of this invention.

The salts defined above are alkaline compounds, or compounds which are converted to alkaline compounds by heat, which attack the polyester molecules at the surface of the filaments upon exposure of the filaments to an elevated temperature. This chemical attack by alkaline materials has been found to be necessary for the prevention of fusion of adjacent filaments when a polyester yarn contacts a hot surface.

Illustrative of the salts which are operable in the process of this invention are the following: sodium hydroxide, sodium acetate, sodium dichloroacetate, sodium trichloroacetate, potassium hydroxide, sodium bicarbonate, sodium oxalate, magnesium hydroxide and calcium acetate. Other salts which may be used include lithium formate, lithium propionate, cesium acetate, rubidium acetate, sodium methoxide, potassium ethoxide, and the like.

Only a minor amount of alkaline salt is required in the process of this invention. Where the salt is added to the spinning finish the amount of salt which may be used is limited somewhat by the stability of the finish. Generally it is desirable to add enough salt to the spinning finish to give a concentration in the range 0.2% to by weight based on the weight of the finish, preferably in the range 0.5 to 5%. The amount of salt deposited on the yarn may range from 0.0002% to 0.5%, based on the weight of the yarn, with the preferred concentration falling in the range 0.002% to 0.05%.

Although the salt is usually applied to the polyester yarn from an aqueous solution, such as an aqueous base spin finish, it is sometimes desirable to use an organic solvent system. For example, the metal alcoholates such as sodium methoxide may be applied to the yarn in the form of a dilute alcoholic solution. The solvent chosen must be a volatile one which may be evaporated from the polyester filament at a relatively low temperature, leaving the dissolved salt on the surfaces of the filaments. Usually solvents which are swelling agents for the fiber are avoided except where their special effects upon yarn properties are desired. Mixtures of solvents may be used if desired.

The degree of success in preventing the fusing of filaments during high temperature processing will be most apparent in the handle of the fabric woven from the yarn. As mentioned previously, fabric handle becomes stiff and boardy as the number of fused or coalesced filaments increases. Conversely, prevention of filament fusing leads to a soft, pleasing fabric handle. The number of fused filaments in the yarn itself may be determined by using a microscope to study yarn cross sections, although this procedure is tedious and time consuming.

A convenient laboratory test for detecting the degree of fusing of filaments in a yarn involves the use of a standard Instron Tensile Testing instrument (sold by Instron Engineering Corp., Canton, Mass). Using this instrument a yarn sample is stretched at a constant rate of elongation and the load, measured by a strain gauge, is recorded on a chart. When a zero-twist multi-filament yarn bundle is broken the stress-strain curve on the chart shows the breaking of each individual filament as a separate pip on the curve. The number of filaments may be determined by counting the individual pips on the curve at the breaking point. Since two filaments which are stuck together will give only a single pip on the curve, the difference between the observed number of pips and the theoretical number of filaments in the yarn is a measure of degree of fusing of filaments. A numerical value for the degree of fusion is calculated by subtracting the number of pips on the Instron curve from the theoretical number of filaments and dividing by the theoretical num- 4 ber of filaments. The percent fusion is calculated by multiplying this fraction by 100,

The numerical values for percent fusion must be interpreted in light of the statistical chance that two or more completely separate filaments in a given yarn bundle may break. at the same time, giving a single pip on the stressstrain curve. Experience indicates that yarns giving a numerical value of 15% fusion, or below, are essentially free of fused filaments.

The followingexamples are illustrative ples and practice of this invention.

of the princi- EXAMPLE It Polyethylene terephth-alate having an intrinsic viscosity of 0.55 is melt spun in a conventional manner using a spinneret temperature of 290 C. and wound up at a speed of 1500 y.p.m. to give a yarn having 27 filaments and an over-all denier of 454. Between the spinneret and the windup the spun yarn contacts a finish roll which applies to the filaments bundle a spinning finish composed of a 2% aqueous emulsion of a light mineral oil emulsified with an anionic surfactant and having dissolved in the aqueous phase 1.3 percent of sodium hydroxide.

The undrawn as-spun yarn prepared above is passed from a feed roller rotating at surface speed of 75 y.p.m. to a heated chrome-plated steel roller rotating at the same surface speed and heated to a temperature of 172 C. The yarn makes a 360 turn around the heated roller, passes to and around a ceramic snubbing pin heated to a temperature of C., and then passes to and around a cold draw roller operating at a surface speed of 454 y.p.m., giving :an over-all draw ratio of 6.048. The drawn yarn is wound up in a conventional manner. The yarn produced is found to have a denier of 75, a tenacity of 2.2 g.p.d. and an elongation at break of 41.5%.

Calculation of the degree of filament fusing from the stress-strain chart obtained by breaking the yarn on an Instron Tensile Tester indicates that the yarn is composed of 9% fused filaments. Examination of yarn cross sec tions under a microscope indicates no fused filaments, as shown in FIGURE 2.

The yarn produced above is woven into a plain weave taffeta fabric and found to have the soft handle exhibited by similar fabrics prepared from polyethylene terephthalate yarn drawn in a more conventional fashion, i.e., at a temperature below the softening temperature of the amorphous unoriented yarn.

When the experiment is repeated without the sodium hydroxide in the spinning finish, the drawn yarn is found to have 70% fused filaments and fabric prepared from the yarn is found to exhibit a stiff and boardy handle. Yarn cross sections examined under a microscope are similar to that of FIGURE 1.

EXAMPLE II Polyethylene terephthalate is melt-spun as in Example I with the exception that the spin finish contains 1.3% sodium acetate instead of sodium hydroxide.

The as-spun yarn is drawn in a two-stage process as follows. The yarn passes around a feed roller rotating at a surface speed of 75 y.p.m., and then around a heated roller operating at the same surface speed and heated to a temperature of 165 C. The yarn then passes to and around an intermediate draw roller operating at a surface speed of 121 y.p.m., then over a hot plate maintained at a temperature of C., then passes around a small ceramic snubbing pin, and then around a final draw roller operating at a surface speed of 454 y.p.m. The drawn yarn is wound up on a zero-twist bobbin.

The dratWn yarn is found to have a tenacity of 3.7 g.p. d., a break elongation of 37%, and an initial modulus of 109 g.p.d. The yarn is woven into a plain weave taffeta fabric and is found to have the soft handle normally associated with polyethylene terephthalate fiber 5, V drawn by the conventional intermediate temperature drawing processes of the prior art.

When the degree of fusing of filaments -is calculated from the stress-stnain curve obtained by breaking yarn on an Instron Tensile Tester, the yarn is found to have 5-11% fused filaments.

When this experiment is repeated without the sodium acetate in the spinning finish, the yarn is found to have 55% fused filaments and fabric woven therefrom possesses a stiff and boardy handle.

EXAMPLE III The procedure of Example I is repeated using polyethylene terephthalate in which there is incorporated 1.15 mol percent of the sodium salt of 3,5-di(carbomethoxy)- benzene sulfonic acid. The drawn yarn produced is found to have approximately 12% fused filaments, whereas yarn produced without the sodium hydroxide in the spin finish is found to have approximately 75% fused filaments (Instron test).

EXAMPLE IV The procedure of Example 11 is repeated with the exception that the salts of Table I are added, in turn, to the spin finish in place of 1.5% sodium acetate. Each drawn yarn is tested for fused filaments in the Instron test previously described, with the results listed in the table. Inspection of the data in the table indicates the remarkable repression of fusing of filaments obtained by the process of this invention.

Table I EFFECT OF ALKALINE SALTS ON FUSING OF FILAMENTS Concentration Percent Salt of Salt Fused in Spin Filaments Finish,

percent None (control) 71 Sodium chloroacetate 1. 3 10 Sodium dichloroaeetate 1. 3 5 Sodium trichloroaeetate 1. 3 11 Sodium acetate 3. 15 Sodium acetate 1.0 Sodium oxalatefln 5 Sodium biearbonat 5 6 Sodium hydroxide, 1. 3 9 Sodium hydro. 'ide 0. 4 17 Potassium hydroxide 1. 3 l1 Magnesium hydroxide 5 24 Calcium acetate 1. 3 30 EXAMPLE V This example illustrates the ineifectiveness of salts of strong or non-volatile acids in achieving the results of the present invention.

The procedure of Example IV is repeated with the salts of Table II added, in turn, to the spin finish. The results of the Instron test for fused filaments are presented in the table. The ineffectiveness of the salts of Table II is obvious from the high values for percent fused filaments in column 3.

While this invention is described with particular reference to polyethylene terephthalate, it is understood that the invention comprehends the treatment of all fiberforming synthetic linear polyesters including the inclusion therein of minor amounts of modifying materials. In the examples the polyester yarn used to illustrate the invention may be substituted by yarns of any of the following polymers with satisfactory results. Of particular importance are the polyesters disclosed by Whinfield and Dickson in US. Patent 2,465,319 prepared from terephthalic acid and glycols of the type HO(CH ),,OH where n is an integer from 2 to 10. Other glycols from which the polyester or copolyester may be prepared include any suitable dihydroxy compound containing from 2 to 18 carbon atoms, preferably from 2 to 10 carbon atoms, in which the hydroxyl groups are attached to saturated carbon atoms. Thus, the glycol molecule may contain a cyclo aliphatic group, an aromatic group, an oxy group or an arylenedioxy group as long as the hydroxyl groups are attached to saturated carbon atoms. Illustrative examples of suitable glycols include the straight chain polymethylene glycols, and branched chain glycols such as 2,2-dimethyl-1,3-propanediol and 2,2-dimethyl-1,4-butanediol. Other suitable glycols include trans-p-hexahydroxylylene glycol, bis-p-(Z-hydroxyethyl) benzene, diethylene glycol, bis-(4-hydroxybutyl)ether, bis p (B-hydroxyethoxy) benzene, bis-1,4-(fi-hydroxyethoxy) -2,5-dichlorobenzene, bis-4,4'- 13-hydroxyethoxy) diplienyl, 2,6-di(fi-hydroxyethoxy) naphthalene, bis-[p- (B hydroxyethoxy)phenyl] ketone, bis- [p-(B-hydroxyethoxy)phenyl] sulphone, and bis-[p-(B-hydroxyethoxy) phenylJ-difluoromethane. Additional glycols which may be used include 4,4'-bis-(pr-hydroxyethyl)biphenyl, 4,4- bis (J3 hydroxyethyl)dodecahydrobiphenyl, triethylene glycol, and 2,2-(ethylene-bis-[p-phenyleneoxy)diethanol. It is understood that mixtures of glycols may be used and that small amounts of polymeric glycols such as polyethylene glycol of high molecular Weight may be added.

In addition to polyesters from terephthalic acid, this invention is also useful in the processing of fiber-forming polyesters from other acids, as Well as mixtures of terephthalic acid with other acids. Illustrative examples of other acids include adipic, sebacic, isophthalic, bibenzoic, hexahydroterephthalic, diphenoxyethane-4,4'-dicarboxylic, p,p'-carbonyldibenzoic, and p,p'-sulfonyldibenzoic. Fiber-forming synthetic linear polyesters may be prepared by reacting a glycol with the free acid or mixture of acids or with a reactive form of the acid such as the dimethyl ester. Among other polyesters which may be treated by the invention may be mentioned:

(1) Polyesters from bisphcnols, such as the isophthalate of 2,2-(4,4-dihydroxydiphenyl)propane.

(2) Polyesters from bisnaphthols, such as the isophthalate of 4,4 dihydroxy 3,3 dichlorodinaphthyl methane.

13) Polyesters from ethylene glycol and 2,6-naphthalic aci Fiber-forming synthetic linear polyesters should possess an intrinsic viscosity of at least 0.3 and preferably should have an intrinsic viscosity of from 0.3-1.5. Synthetic linear polyesters having intrinsic viscosities ofless than 0.3 do not form commercially acceptable fibers. The transition temperatures and degradation temperatures are too low to be useful and, furthermore the physical and chemical properties of fibers made from such low molecular weight materials are not in the useful range insofar as technical purposes are concerned. Intrinsic viscosity may be determined as in US. 2,744,087.

It will be apparent that many widely different embodiments of this invention may be made Without departing from the spirit and scope thereof, and, therefore, it is not intended to be limited except as indicated in the appended claims.

I claim:

1. The process of preventing the fusion of solid undrawn amorphous synthetic linear polyester filaments in which the ester groups of the polyester are in the polymer chain, said filaments being those which normally fuse on contact when hot, which comprises depositing on the surface of the said undrawn filaments a compound selected from the class consisting of the hydroxides and salts or weak acids the cation of which is a metal selected from the group consisting of the alkali metals and alkaline-earth metals and the anion of which is one of an acid which is removable at least in part at a temperature below the melting point of the said filaments.

2. The process of claim 1 in which the said compound is sodium hydroxide.

3. The process of claim 1 in which the said compound is sodium acetate.

4. The process of claim 1 in which the said compound is applied in a liquid medium having a concentration of from 0.2% to 10% by weight of the said compound.

5. Tl e process of claim 4 in which the concentration is from 0.5% to 5%.

6. The process of claim 1 in which the amount of the said compound deposited on the yarn is from 0.0002% to 0.5% based on the weight of the yarn.

7. The process of claim 6 in which the amount of compound deposited on the yarn is from 0.002% to 0.05% by weight.

8. The process of claim 1 in which the compound is a salt of an acid having an ionization constant of less than 0.25

9. The process of claim 1 in which the yarn is made from polyethylene terephthalate.

References Cited in the file of this patent UNITED STATES PATENTS 2,395,396 Conaway Feb. 26, 1946 2,578,899 Pace Dec. 18, 1951 2,590,402 Hall et al Mar. 25, 1952 2,718,47 8 Pluck et al Sept. 20, 1955 2,781,242 Knapp Feb. 12, 1957 2,828,528 Gajjar Apr. 1, 1958 2,938,823 Salem et al May 31, 1960 2,998,296 Hennemann Aug. 29, 1961 

1. THE PROCESS OF PREVENTING THE FUSION OF SOLID UNDRAWN AMORPHOUS SYNTHETIC LINEAR POLYESTER FILAMENTS IN WHICH THE ESTER GROUPS OF THE JPOLYESTER ARE IN THE POLYMER CHAIN, SAID FILAMENTS BEING THOSE WHICH NORMALLY FUSE ON CONTACT WHEN HOT, WHICH COMPRISES DEPOSITING ON THE SURFACE OF THE SAID UNDRAWN FILAMENTS A COMPOUND SELECTED FROM THE CLASS CONSISTING OF THE HYDROXIDES AND SALTS OF WEAK ACIDS THE CATION OF WHICH IS A METAL SELECTED FROM THE GROUP CONSISTING OF THE ALKALI METALS AND ALKALINE-EARTH METALS AND THE ANION OF WHICH IS ONE OF AN ACID WHICH IS REMOVABLE AT LEAST IN PART AT A TEMPERATURE BELOW THE MELTING JPOINT OF THE SAID FILAMENTS. 